First thing in the morning, you can physically engage your students with a greeting. Be sure to focus on the student (don't be distracted or multi-task), use eye contact, ask a question, smile!
What if you're too busy right when the students come in? This will happen occasionally, though you should plan in advance and be sure that greeting is a priority for you. But, if you are distracted, be sure your Do Now is on the board, and while the students are working, go to each desk or table and personally greet them..
Give it a try and see if it makes a difference in your classroom environment.